The present invention relates to a detector used for spectrometry, and especially, to a detector which is suitable for measuring a wide wavelength region by using an integrating sphere with a high sensitivity at high response speed. Also, the present invention relates to a spectrophotometer which conducts a measurement by using the integrating sphere.
Conventionally, as one method for spectrometry, a measurement using an integrating sphere has been carried out. In case the spectrometry is conducted in a wide wavelength region by using the integrating sphere, two or more detectors which are respectively suitable for a short wavelength area and a long wavelength area are attached to the integrating sphere. As a combination of these detectors, a photomultiplier (PM) used for the short wavelength side and a PbS detector (PbS) used for the long wavelength side have been well known.
FIG. 4 shows a structure of a conventional spectrophotometer in case transmittance is measured by using an integrating sphere. In the figure, numeral 1 designates a light source; numeral 2 designates a spectroscope for dividing a light from the light source into respective wavelengths; numeral 3 designates a sample to which the divided light is irradiated to carry out a measurement of transmittance; and numeral 4 designates a sample light which is transmitted through the sample. The sample light is led to an integrating sphere 5.
In the integrating sphere 5, there are formed an entrance window 6 for leading the sample light 4 to an inside of the integrating sphere 5, and light outgoing windows 7 for leading the light scattered in multiple in the integrating sphere to a photomultiplier (PM) and a PbS detector (PbS). Numeral 8 designates the photomultiplier (PM) attached to one of the light outgoing windows, and numeral 9 designates the PbS detector (PbS) attached to the other light outgoing window. Numeral 10 designates an amplifier which amplifies a detected signal from the photomultiplier (PM) or the PbS detector (PbS), numeral 11 designates an analog-to-digital converter, and numeral 12 designates a change-over switch for switching to determine which one of the signals from the detectors is outputted to outside.
When the sample light 4 is introduced into the integrating sphere 5 from the light incoming window 6, the light is subjected to the multiple scattering to reach the light outgoing window 7. When the scattered light is received at the photomultiplier 8 or PbS detector 9, the light is detected, and outputted to outside (a personal computer for data processing connected in a subsequent stage) via the amplifier 10 and analog-to-digital converter 11. Then, by switching the change-over switch 12 in accordance with the measured wavelength area, a signal from one of the detectors is sent out.
In the aforementioned detectors, the PbS detector 9 is used as a detector for a near-infrared region. Although the PbS detector 9 is advantageous in that the PbS detector can be used in a wide wavelength range of the near-infrared region, the spectral sensitivity characteristic of the PbS detector is inferior to that of a near-infrared detector using other semiconductor elements. Also, a response speed of the PbS detector is relatively slow. Therefore, the PbS detector is not suitable for a measurement with the high response speed.
Thus, in order to improve the sensitivity in the near-infrared region, or in order to conduct the measurement with the high response speed, it is necessary to use a detector other than the PbS detector. However, so far, there is no appropriate detector which has a high spectral sensitivity characteristic throughout the wide wavelength range in the near-infrared region and which can be used in the spectrophotometer. Thus, in order to carry out the measurement for the wide wavelength range of the near-infrared with the high sensitivity, it is necessary to attach two or more near-infrared detectors having different spectral sensitivity characteristics to the integrating sphere, wherein these detectors are switched in use.
FIGS. 2(a)-2(c) show an integrating sphere provided with two near-infrared detectors. In FIGS. 2(a)-2(c), the components which are the same as those in FIG. 4 are designated by the same numeral references, so that explanations therefor are omitted herewith. In the integrating sphere 5, as detectors for the near-infrared region, a first detector 15 and a second detector 16 are respectively attached to the light outgoing windows 7.
In the first detector 15, there is attached a first semiconductor element 31 having a high sensitivity range in a relatively shorter wavelength side among the near-infrared, and in the second detector 16, there is attached a second semiconductor element 32 having a high sensitivity range in a wavelength side longer than that of the semiconductor element used in the first detector. As a combination of these elements, there can be considered a combination in which Si (silicon) is used in the first semiconductor element, and InGaAs is used in the second semiconductor element. Also, as another example, there can be considered a combination in which InGaAs is used both in the first semiconductor 31 and the second semiconductor 32, but high sensitivity wavelength ranges of these semiconductor elements are different by changing the composition ratio thereof.
The device shown in FIGS. 2(a)-2(c) is excellent in the response speed and sensitivity. However, it is necessary to provide two light outgoing windows for the near-infrared region in the integrating sphere. Since a performance of the integrating sphere becomes better as an area occupied by the windows as opening sections becomes smaller, if the number of the windows is increased, the performance of the integrating sphere is deteriorated. Of course, if the area of each window can be reduced, the above problem might be solved. However, since packages of the detectors are required to be attached to the windows to lead the measurement light to the detector, there is a limit to reduce each of the areas of the windows. Thus, in order to increase the performance of the integrating sphere, it is necessary to reduce the number of the light outgoing windows, and it is also necessary to have only one near-infrared detector.
Therefore, as shown in FIGS. 3(a)-3(c), it is considered to use a transmission type compound detector 17 as a detector. The transmission type compound detector 17 has a laminate structure in which a first semiconductor detection element 33 and a second semiconductor detection element 34 are laminated, and a light in the same optical path can be detected by the two different kinds of the detection elements. For example, a transmission type compound detector has been available on the market, wherein Si (silicon) is used as the first semiconductor element and Ge or InGaAs are used as the second semiconductor element.
In this type of the detector, since optical paths of the two elements are the same, only light transmitted through the first semiconductor detection element in a front side reaches the second semiconductor detection element in a rear side. Namely, regarding the detection element in the rear side, even in case light in a range of wavelengths for which the spectral sensitivity characteristic of the rear detection element is good is irradiated, if the light with the wavelengths is absorbed at the detection element in the front side, the light reaches the detection element in the rear side after loss in a quantity of light occurs at the front side, resulting in that the measurement with high sensitivity is difficult. In other words, when the maximum sensitivity wavelengths of both detection elements are close to each other, the loss in quantity of the light reaching the second semiconductor detection element occurs, so that the effective measurement can not be carried out.
Therefore, in order to effectively use the transmission type compound detector, it is necessary that the maximum sensitivity wavelengths of the detection elements are different and away from each other. When the two detection elements having the maximum sensitivity wavelengths extremely away from each other are combined, consequentially, a low sensitivity region appears in an intermediate wavelength range between the maximum sensitivity wavelengths of the detection elements. Therefore, even if the transmission type compound detector is used, it is difficult to carry out the high sensitivity measurement in the wide wavelength range of the near-infrared region.
As described above, due to the structure of the conventional detector, it is difficult to carry out the high sensitivity measurement while the performance of the integrating sphere is maintained, that is, without increasing the number of the windows in the integrating sphere.
Accordingly, an object of the invention is to provide a detector for spectrometry and an integrating sphere measurement device using the detector, in which a structure of the detector is contrived to enable the high sensitivity measurement while the performance of the integrating sphere is maintained.
Further objects and advantages of the invention will be apparent from the following description of the invention.
To achieve the aforementioned object, the present invention provides a detector for spectrometry, in which a plurality of detection elements having different spectral sensitivity characteristics is arranged in a planar direction, i.e. side by side, on a base as a light receiving surface, and stored in one package including a light receiving window.
As the detection elements having different spectral sensitivity characteristics used in the detector, semiconductor detection elements are suitable since the semiconductor detection elements have a high response speed and an excellent sensitivity characteristic even in a small area. As a combination of the semiconductor detection elements, there can be a combination of semiconductor detection elements in which semiconductor materials themselves are different, or a combination of semiconductor detection elements in which the semiconductor materials are the same but the composition ratios thereof are different.
Incidentally, although a detector, such as a photodiode array detector (PDA), in which a plurality of detection elements having the same spectral sensitivity characteristics is arranged on the plane, is available on the market, this kind of the detector is not included in the detector of the invention. In the first place, the PDA is used for the purpose of measuring a spatial (positional) distribution of quantity of light, and is not provided for detecting light in a single optical path, such as light from a light outgoing window of the integrating sphere.
Two or more detection elements are arranged side by side on the plane of the base, and in order to shield the unnecessary light from the outside and guide only the sample light from one direction to the base as the light receiving surface, the detection elements are stored in a package. Since any detection elements can directly receive the sample light by arranging the detection elements in the plane, there is no problem that the quantity of light is lost at the detection element in the rear side of the transmission type compound detector as shown in FIG. 3(a).
Further, the detector for spectrometry described above is attached to one light outgoing window of the integrating sphere, and only the measurement light from the light outgoing window of the integrating sphere is directly irradiated to the respective two or more detection elements placed on the base.
Therefore, when the sample light enters into the integrating sphere from the light incoming window of the integrating sphere, multiple scattering of the light occurs in the integrating sphere, and the light is irradiated from the light outgoing window to the respective detection elements and converted into electric signals to issue detection signals. Thus, by selecting the signal from the appropriate detection element in accordance with the measured wavelength area to take out the same, the spectrometry with the high sensitivity using the integrating sphere can be carried out.